OK, let's crack this. We're given 644 and our task is to multiply it by 427. Essentially, we'll be adding 644 to itself 427 times.
Step 1: 0 + 644 = 644
Step 2: 644 + 644 = 1288
Step 3: 1288 + 644 = 1932
Step 4: 1932 + 644 = 2576
Step 5: 2576 + 644 = 3220
Step 6: 3220 + 644 = 3864
Step 7: 3864 + 644 = 4508
Step 8: 4508 + 644 = 5152
Step 9: 5152 + 644 = 5796
Step 10: 5796 + 644 = 6440
Step 11: 6440 + 644 = 7084
Step 12: 7084 + 644 = 7728
Step 13: 7728 + 644 = 8372
Step 14: 8372 + 644 = 9016
Step 15: 9016 + 644 = 9660
Step 16: 9660 + 644 = 10304
Step 17: 10304 + 644 = 10948
Step 18: 10948 + 644 = 11592
Step 19: 11592 + 644 = 12236
Step 20: 12236 + 644 = 12880
Step 21: 12880 + 644 = 13524
Step 22: 13524 + 644 = 14168
Step 23: 14168 + 644 = 14812
Step 24: 14812 + 644 = 15456
Step 25: 15456 + 644 = 16100
Step 26: 16100 + 644 = 16744
Step 27: 16744 + 644 = 17388
Step 28: 17388 + 644 = 18032
Step 29: 18032 + 644 = 18676
Step 30: 18676 + 644 = 19320
Step 31: 19320 + 644 = 19964
Step 32: 19964 + 644 = 20608
Step 33: 20608 + 644 = 21252
Step 34: 21252 + 644 = 21896
Step 35: 21896 + 644 = 22540
Step 36: 22540 + 644 = 23184
Step 37: 23184 + 644 = 23828
Step 38: 23828 + 644 = 24472
Step 39: 24472 + 644 = 25116
Step 40: 25116 + 644 = 25760
Step 41: 25760 + 644 = 26404
Step 42: 26404 + 644 = 27048
Step 43: 27048 + 644 = 27692
Step 44: 27692 + 644 = 28336
Step 45: 28336 + 644 = 28980
Step 46: 28980 + 644 = 29624
Step 47: 29624 + 644 = 30268
Step 48: 30268 + 644 = 30912
Step 49: 30912 + 644 = 31556
Step 50: 31556 + 644 = 32200
Step 51: 32200 + 644 = 32844
Step 52: 32844 + 644 = 33488
Step 53: 33488 + 644 = 34132
Step 54: 34132 + 644 = 34776
Step 55: 34776 + 644 = 35420
Step 56: 35420 + 644 = 36064
Step 57: 36064 + 644 = 36708
Step 58: 36708 + 644 = 37352
Step 59: 37352 + 644 = 37996
Step 60: 37996 + 644 = 38640
Step 61: 38640 + 644 = 39284
Step 62: 39284 + 644 = 39928
Step 63: 39928 + 644 = 40572
Step 64: 40572 + 644 = 41216
Step 65: 41216 + 644 = 41860
Step 66: 41860 + 644 = 42504
Step 67: 42504 + 644 = 43148
Step 68: 43148 + 644 = 43792
Step 69: 43792 + 644 = 44436
Step 70: 44436 + 644 = 45080
Step 71: 45080 + 644 = 45724
Step 72: 45724 + 644 = 46368
Step 73: 46368 + 644 = 47012
Step 74: 47012 + 644 = 47656
Step 75: 47656 + 644 = 48300
Step 76: 48300 + 644 = 48944
Step 77: 48944 + 644 = 49588
Step 78: 49588 + 644 = 50232
Step 79: 50232 + 644 = 50876
Step 80: 50876 + 644 = 51520
Step 81: 51520 + 644 = 52164
Step 82: 52164 + 644 = 52808
Step 83: 52808 + 644 = 53452
Step 84: 53452 + 644 = 54096
Step 85: 54096 + 644 = 54740
Step 86: 54740 + 644 = 55384
Step 87: 55384 + 644 = 56028
Step 88: 56028 + 644 = 56672
Step 89: 56672 + 644 = 57316
Step 90: 57316 + 644 = 57960
Step 91: 57960 + 644 = 58604
Step 92: 58604 + 644 = 59248
Step 93: 59248 + 644 = 59892
Step 94: 59892 + 644 = 60536
Step 95: 60536 + 644 = 61180
Step 96: 61180 + 644 = 61824
Step 97: 61824 + 644 = 62468
Step 98: 62468 + 644 = 63112
Step 99: 63112 + 644 = 63756
Step 100: 63756 + 644 = 64400
Step 101: 64400 + 644 = 65044
Step 102: 65044 + 644 = 65688
Step 103: 65688 + 644 = 66332
Step 104: 66332 + 644 = 66976
Step 105: 66976 + 644 = 67620
Step 106: 67620 + 644 = 68264
Step 107: 68264 + 644 = 68908
Step 108: 68908 + 644 = 69552
Step 109: 69552 + 644 = 70196
Step 110: 70196 + 644 = 70840
Step 111: 70840 + 644 = 71484
Step 112: 71484 + 644 = 72128
Step 113: 72128 + 644 = 72772
Step 114: 72772 + 644 = 73416
Step 115: 73416 + 644 = 74060
Step 116: 74060 + 644 = 74704
Step 117: 74704 + 644 = 75348
Step 118: 75348 + 644 = 75992
Step 119: 75992 + 644 = 76636
Step 120: 76636 + 644 = 77280
Step 121: 77280 + 644 = 77924
Step 122: 77924 + 644 = 78568
Step 123: 78568 + 644 = 79212
Step 124: 79212 + 644 = 79856
Step 125: 79856 + 644 = 80500
Step 126: 80500 + 644 = 81144
Step 127: 81144 + 644 = 81788
Step 128: 81788 + 644 = 82432
Step 129: 82432 + 644 = 83076
Step 130: 83076 + 644 = 83720
Step 131: 83720 + 644 = 84364
Step 132: 84364 + 644 = 85008
Step 133: 85008 + 644 = 85652
Step 134: 85652 + 644 = 86296
Step 135: 86296 + 644 = 86940
Step 136: 86940 + 644 = 87584
Step 137: 87584 + 644 = 88228
Step 138: 88228 + 644 = 88872
Step 139: 88872 + 644 = 89516
Step 140: 89516 + 644 = 90160
Step 141: 90160 + 644 = 90804
Step 142: 90804 + 644 = 91448
Step 143: 91448 + 644 = 92092
Step 144: 92092 + 644 = 92736
Step 145: 92736 + 644 = 93380
Step 146: 93380 + 644 = 94024
Step 147: 94024 + 644 = 94668
Step 148: 94668 + 644 = 95312
Step 149: 95312 + 644 = 95956
Step 150: 95956 + 644 = 96600
Step 151: 96600 + 644 = 97244
Step 152: 97244 + 644 = 97888
Step 153: 97888 + 644 = 98532
Step 154: 98532 + 644 = 99176
Step 155: 99176 + 644 = 99820
Step 156: 99820 + 644 = 100464
Step 157: 100464 + 644 = 101108
Step 158: 101108 + 644 = 101752
Step 159: 101752 + 644 = 102396
Step 160: 102396 + 644 = 103040
Step 161: 103040 + 644 = 103684
Step 162: 103684 + 644 = 104328
Step 163: 104328 + 644 = 104972
Step 164: 104972 + 644 = 105616
Step 165: 105616 + 644 = 106260
Step 166: 106260 + 644 = 106904
Step 167: 106904 + 644 = 107548
Step 168: 107548 + 644 = 108192
Step 169: 108192 + 644 = 108836
Step 170: 108836 + 644 = 109480
Step 171: 109480 + 644 = 110124
Step 172: 110124 + 644 = 110768
Step 173: 110768 + 644 = 111412
Step 174: 111412 + 644 = 112056
Step 175: 112056 + 644 = 112700
Step 176: 112700 + 644 = 113344
Step 177: 113344 + 644 = 113988
Step 178: 113988 + 644 = 114632
Step 179: 114632 + 644 = 115276
Step 180: 115276 + 644 = 115920
Step 181: 115920 + 644 = 116564
Step 182: 116564 + 644 = 117208
Step 183: 117208 + 644 = 117852
Step 184: 117852 + 644 = 118496
Step 185: 118496 + 644 = 119140
Step 186: 119140 + 644 = 119784
Step 187: 119784 + 644 = 120428
Step 188: 120428 + 644 = 121072
Step 189: 121072 + 644 = 121716
Step 190: 121716 + 644 = 122360
Step 191: 122360 + 644 = 123004
Step 192: 123004 + 644 = 123648
Step 193: 123648 + 644 = 124292
Step 194: 124292 + 644 = 124936
Step 195: 124936 + 644 = 125580
Step 196: 125580 + 644 = 126224
Step 197: 126224 + 644 = 126868
Step 198: 126868 + 644 = 127512
Step 199: 127512 + 644 = 128156
Step 200: 128156 + 644 = 128800
Step 201: 128800 + 644 = 129444
Step 202: 129444 + 644 = 130088
Step 203: 130088 + 644 = 130732
Step 204: 130732 + 644 = 131376
Step 205: 131376 + 644 = 132020
Step 206: 132020 + 644 = 132664
Step 207: 132664 + 644 = 133308
Step 208: 133308 + 644 = 133952
Step 209: 133952 + 644 = 134596
Step 210: 134596 + 644 = 135240
Step 211: 135240 + 644 = 135884
Step 212: 135884 + 644 = 136528
Step 213: 136528 + 644 = 137172
Step 214: 137172 + 644 = 137816
Step 215: 137816 + 644 = 138460
Step 216: 138460 + 644 = 139104
Step 217: 139104 + 644 = 139748
Step 218: 139748 + 644 = 140392
Step 219: 140392 + 644 = 141036
Step 220: 141036 + 644 = 141680
Step 221: 141680 + 644 = 142324
Step 222: 142324 + 644 = 142968
Step 223: 142968 + 644 = 143612
Step 224: 143612 + 644 = 144256
Step 225: 144256 + 644 = 144900
Step 226: 144900 + 644 = 145544
Step 227: 145544 + 644 = 146188
Step 228: 146188 + 644 = 146832
Step 229: 146832 + 644 = 147476
Step 230: 147476 + 644 = 148120
Step 231: 148120 + 644 = 148764
Step 232: 148764 + 644 = 149408
Step 233: 149408 + 644 = 150052
Step 234: 150052 + 644 = 150696
Step 235: 150696 + 644 = 151340
Step 236: 151340 + 644 = 151984
Step 237: 151984 + 644 = 152628
Step 238: 152628 + 644 = 153272
Step 239: 153272 + 644 = 153916
Step 240: 153916 + 644 = 154560
Step 241: 154560 + 644 = 155204
Step 242: 155204 + 644 = 155848
Step 243: 155848 + 644 = 156492
Step 244: 156492 + 644 = 157136
Step 245: 157136 + 644 = 157780
Step 246: 157780 + 644 = 158424
Step 247: 158424 + 644 = 159068
Step 248: 159068 + 644 = 159712
Step 249: 159712 + 644 = 160356
Step 250: 160356 + 644 = 161000
Step 251: 161000 + 644 = 161644
Step 252: 161644 + 644 = 162288
Step 253: 162288 + 644 = 162932
Step 254: 162932 + 644 = 163576
Step 255: 163576 + 644 = 164220
Step 256: 164220 + 644 = 164864
Step 257: 164864 + 644 = 165508
Step 258: 165508 + 644 = 166152
Step 259: 166152 + 644 = 166796
Step 260: 166796 + 644 = 167440
Step 261: 167440 + 644 = 168084
Step 262: 168084 + 644 = 168728
Step 263: 168728 + 644 = 169372
Step 264: 169372 + 644 = 170016
Step 265: 170016 + 644 = 170660
Step 266: 170660 + 644 = 171304
Step 267: 171304 + 644 = 171948
Step 268: 171948 + 644 = 172592
Step 269: 172592 + 644 = 173236
Step 270: 173236 + 644 = 173880
Step 271: 173880 + 644 = 174524
Step 272: 174524 + 644 = 175168
Step 273: 175168 + 644 = 175812
Step 274: 175812 + 644 = 176456
Step 275: 176456 + 644 = 177100
Step 276: 177100 + 644 = 177744
Step 277: 177744 + 644 = 178388
Step 278: 178388 + 644 = 179032
Step 279: 179032 + 644 = 179676
Step 280: 179676 + 644 = 180320
Step 281: 180320 + 644 = 180964
Step 282: 180964 + 644 = 181608
Step 283: 181608 + 644 = 182252
Step 284: 182252 + 644 = 182896
Step 285: 182896 + 644 = 183540
Step 286: 183540 + 644 = 184184
Step 287: 184184 + 644 = 184828
Step 288: 184828 + 644 = 185472
Step 289: 185472 + 644 = 186116
Step 290: 186116 + 644 = 186760
Step 291: 186760 + 644 = 187404
Step 292: 187404 + 644 = 188048
Step 293: 188048 + 644 = 188692
Step 294: 188692 + 644 = 189336
Step 295: 189336 + 644 = 189980
Step 296: 189980 + 644 = 190624
Step 297: 190624 + 644 = 191268
Step 298: 191268 + 644 = 191912
Step 299: 191912 + 644 = 192556
Step 300: 192556 + 644 = 193200
Step 301: 193200 + 644 = 193844
Step 302: 193844 + 644 = 194488
Step 303: 194488 + 644 = 195132
Step 304: 195132 + 644 = 195776
Step 305: 195776 + 644 = 196420
Step 306: 196420 + 644 = 197064
Step 307: 197064 + 644 = 197708
Step 308: 197708 + 644 = 198352
Step 309: 198352 + 644 = 198996
Step 310: 198996 + 644 = 199640
Step 311: 199640 + 644 = 200284
Step 312: 200284 + 644 = 200928
Step 313: 200928 + 644 = 201572
Step 314: 201572 + 644 = 202216
Step 315: 202216 + 644 = 202860
Step 316: 202860 + 644 = 203504
Step 317: 203504 + 644 = 204148
Step 318: 204148 + 644 = 204792
Step 319: 204792 + 644 = 205436
Step 320: 205436 + 644 = 206080
Step 321: 206080 + 644 = 206724
Step 322: 206724 + 644 = 207368
Step 323: 207368 + 644 = 208012
Step 324: 208012 + 644 = 208656
Step 325: 208656 + 644 = 209300
Step 326: 209300 + 644 = 209944
Step 327: 209944 + 644 = 210588
Step 328: 210588 + 644 = 211232
Step 329: 211232 + 644 = 211876
Step 330: 211876 + 644 = 212520
Step 331: 212520 + 644 = 213164
Step 332: 213164 + 644 = 213808
Step 333: 213808 + 644 = 214452
Step 334: 214452 + 644 = 215096
Step 335: 215096 + 644 = 215740
Step 336: 215740 + 644 = 216384
Step 337: 216384 + 644 = 217028
Step 338: 217028 + 644 = 217672
Step 339: 217672 + 644 = 218316
Step 340: 218316 + 644 = 218960
Step 341: 218960 + 644 = 219604
Step 342: 219604 + 644 = 220248
Step 343: 220248 + 644 = 220892
Step 344: 220892 + 644 = 221536
Step 345: 221536 + 644 = 222180
Step 346: 222180 + 644 = 222824
Step 347: 222824 + 644 = 223468
Step 348: 223468 + 644 = 224112
Step 349: 224112 + 644 = 224756
Step 350: 224756 + 644 = 225400
Step 351: 225400 + 644 = 226044
Step 352: 226044 + 644 = 226688
Step 353: 226688 + 644 = 227332
Step 354: 227332 + 644 = 227976
Step 355: 227976 + 644 = 228620
Step 356: 228620 + 644 = 229264
Step 357: 229264 + 644 = 229908
Step 358: 229908 + 644 = 230552
Step 359: 230552 + 644 = 231196
Step 360: 231196 + 644 = 231840
Step 361: 231840 + 644 = 232484
Step 362: 232484 + 644 = 233128
Step 363: 233128 + 644 = 233772
Step 364: 233772 + 644 = 234416
Step 365: 234416 + 644 = 235060
Step 366: 235060 + 644 = 235704
Step 367: 235704 + 644 = 236348
Step 368: 236348 + 644 = 236992
Step 369: 236992 + 644 = 237636
Step 370: 237636 + 644 = 238280
Step 371: 238280 + 644 = 238924
Step 372: 238924 + 644 = 239568
Step 373: 239568 + 644 = 240212
Step 374: 240212 + 644 = 240856
Step 375: 240856 + 644 = 241500
Step 376: 241500 + 644 = 242144
Step 377: 242144 + 644 = 242788
Step 378: 242788 + 644 = 243432
Step 379: 243432 + 644 = 244076
Step 380: 244076 + 644 = 244720
Step 381: 244720 + 644 = 245364
Step 382: 245364 + 644 = 246008
Step 383: 246008 + 644 = 246652
Step 384: 246652 + 644 = 247296
Step 385: 247296 + 644 = 247940
Step 386: 247940 + 644 = 248584
Step 387: 248584 + 644 = 249228
Step 388: 249228 + 644 = 249872
Step 389: 249872 + 644 = 250516
Step 390: 250516 + 644 = 251160
Step 391: 251160 + 644 = 251804
Step 392: 251804 + 644 = 252448
Step 393: 252448 + 644 = 253092
Step 394: 253092 + 644 = 253736
Step 395: 253736 + 644 = 254380
Step 396: 254380 + 644 = 255024
Step 397: 255024 + 644 = 255668
Step 398: 255668 + 644 = 256312
Step 399: 256312 + 644 = 256956
Step 400: 256956 + 644 = 257600
Step 401: 257600 + 644 = 258244
Step 402: 258244 + 644 = 258888
Step 403: 258888 + 644 = 259532
Step 404: 259532 + 644 = 260176
Step 405: 260176 + 644 = 260820
Step 406: 260820 + 644 = 261464
Step 407: 261464 + 644 = 262108
Step 408: 262108 + 644 = 262752
Step 409: 262752 + 644 = 263396
Step 410: 263396 + 644 = 264040
Step 411: 264040 + 644 = 264684
Step 412: 264684 + 644 = 265328
Step 413: 265328 + 644 = 265972
Step 414: 265972 + 644 = 266616
Step 415: 266616 + 644 = 267260
Step 416: 267260 + 644 = 267904
Step 417: 267904 + 644 = 268548
Step 418: 268548 + 644 = 269192
Step 419: 269192 + 644 = 269836
Step 420: 269836 + 644 = 270480
Step 421: 270480 + 644 = 271124
Step 422: 271124 + 644 = 271768
Step 423: 271768 + 644 = 272412
Step 424: 272412 + 644 = 273056
Step 425: 273056 + 644 = 273700
Step 426: 273700 + 644 = 274344
Step 427: 274344 + 644 = 274988

So, 644*427 = 274988